I'm gonna try and help you out here a bit with some edits.
Here's the transformation:
And a Still of the final redux:
Your version looks like a couple of random rectangles that are stuck together with tape ^_^ First thing I did was go back to flat colors, so we can work with a blank slate more or less. Your version used 14 colors, which is WAY more than you needed for a nigh-upon monochrome robot. Next, I redesigned the head shape, to give it some real form, something a bit more recognizable as a helmet/robot head. Then, I redid the body shape. Again, we just had basically a rectangle there, nothing very noticeable or eye catching. This is where I had to start thinking about the _function_ of the robot.
Now, near as I could tell, your robot had a giant gun strapped to his chest. Or rather, superglued from the looks of it. The first thing I did was redesign it so that it was a bit more recognizable as a gun, then I added a mounting bracket (the little bump between the barrel and his body). Believe it or not, there was even a reason for the shape of his body. Our robot buddy here is sitting on a repulsor, so he can't ground himself before the gun fires. Judging by the size, I'd say that gun packs a kick. So, I angled the back so that I'd have room for a stabalizer.
Next came details. A wrap around mount for the gun, complete with rivets to hold it in place, a random panel in the back for prettiness, the stablizer nozzel on his back, and the repulsor complete with a couple panels to make it more visually interesting.
Next came highlighting and shadows. Note, I only used one color for each. You've got to really think about where your lighting is coming from. In this case, it was easy enough to pick a forward light source and run with that. If you look closely at the pixels, you can see I added a bit more detail using just the shadow and highlight color to give some visual intrest to him.
Finally, the repulsor's jet. If you look real close, I added the secondary color using the second to lightest color from the jet.
So on the final version, you've got something that's visually interesting, has depth, and has a color pallet of 8 colors (three for the jet, four for the body, and one for the background(transparent)). It's memory friendly and fun to look at.
the key to this is to _plan_ what you're going to do before you pixel it. Start playing around with ideas on paper before you touch a mouse, then, once you've got a good idea of what you want, start pixeling. Keep in mind you light source and what the thing is going to do. If it's going to have a force, like the cannon, you'll need a counter force (like the stabalizer nozzel), if you're going to have something that flies, it needs to be aerodynamic, if you're going to have a rock crusher, it needs to be big and bulky. I can boil this whole thing down into three words: "Plan your picture."
Anyway, don't take my revision and use it. Do your own revision. You won't learn by grabbing my stuff, you'll only learn if you do.
Just for grins and giggles, here's a couple animations I made with my revision, to give you an idea of what I had in mind:
For the animations, I also strayed away from the black line to give it more depth, turning it into a darker brown color.
Anyway, I hope this helps. Keep it up, you'll get there
stray.. .
